WASHINGTON — President Donald Trump called Saudi Arabia’s new crown prince Wednesday as the U.S. stepped up efforts to mediate a crisis between Qatar and America’s closest regional allies.

The president called Crown Prince Mohammed bin Salman after Saudi Arabia’s King Salman appointed his 31-year-old son as crown prince. The elevation places Mohammed bin Salman as first-in-line to the throne and removed the country’s counterterrorism czar and a figure well-known to Washington from the line of succession.

The White House said in a statement that the two leaders expressed their shared commitment to “cutting off all support for terrorists and extremists, as well as how to resolve the ongoing dispute with Qatar.”

Several members of the Gulf Cooperation Council, including Saudi Arabia, recently cut ties with Qatar, accusing it of funding extremism. Trump injected the U.S. into the volatile crisis among America’s Mideast allies, siding with Saudi Arabia and other countries against Qatar.

Secretary of State Rex Tillerson said Wednesday that Saudi Arabia, the United Arab Emirates, Egypt and Bahrain have prepared a list of demands to submit to Qatar in an effort to defuse ongoing tensions.

“We hope the list of demands will soon be presented to Qatar and will be reasonable and actionable,” Tillerson said in a statement. “We support the Kuwaiti mediation effort and look forward to this matter moving toward a resolution.”

The dispute threatens to disrupt efforts to defeat the Islamic State group and counter Iran.

Earlier this month, Trump appeared to endorse the accusation that the small, gas-rich emirate funds terrorist groups, a serious allegation against a strategic U.S. partner that hosts a base with some 10,000 American troops.

He tweeted that he’d told the kings, presidents and prime ministers he met in Saudi Arabia that funding “Radical Ideology” can’t be tolerated, and “Leaders pointed to Qatar – look!”

Trump also sought to cast the anti-Qatar action led by the Saudis and the United Arab Emirates as the result of his trip last month to Riyadh, where he pressed leaders from dozens of Arab and Muslim governments, including Qatar’s emir, to combat extremism.

Trump and Salman also discussed efforts to achieve peace between Israel and the Palestinians. Trump’s son-in-law and top adviser, Jared Kushner, was in Israel Wednesday for meetings with Israeli and Palestinian leaders in his attempt to revive long-dormant peace talks.

Trump has been working to thaw the U.S.-Saudi relationship, which had setbacks under the Obama administration over its nuclear deal with Iran, something Trump has staunchly condemned.

The kingdom was the first stop on Trump’s maiden overseas trip as president, making him the first U.S. president to make a Muslim country the destination of his first official trip.

Mohammed bin Salman and Trump have already established a working rapport, the two men meeting in Washington earlier this year, and then again during Trump’s visit to Saudi Arabia last month.